1. Field of the Invention
The present invention relates to an insulation-operating rod for use in switchgears in an electric power system such as power generation and/or transformation, and more specifically to an insulation-operating rod suited for porcelain-clad type circuit breakers.
2. Background of the Invention
FIG. 5 is a sectional view of a conventional insulation-operating rod disclosed in the Japanese Patent Publication (unexamined) No. 318415/1994. In FIG. 5, reference numeral 2 is a cylindrical insulating rod which is, for example, formed into a cylindrical shape by impregnating glass fibers with a thermosetting resin. This insulating rod is provided with internal thread 24 on the internal surface and external thread 25 on the external surface of two ends thereof. Numerals 7 and 8 are connecting rods. The connecting rod 7 is provided with a hemispherical shield portion 74 on one end thereof, and an external thread 71 threadably engaging with the internal thread 24 of the insulating rod 2. The connecting rod 7 is also provided with a flange 73 coming in contact with an end of the insulating rod 2 between the main body of the connecting rod 72 and the external thread 71.
The connecting rod 8 is provided with an external thread 81 threadably engaging with the insulating rod 2, a flange 83 coming in contact with another end of the insulating rod 2, an internal thread 82 along the axis of the connecting rod 8. Main body of a connecting rod 84 threadably engages with the internal thread 82. Numeral 9 is a connector provided with a through hole 93 at a bottom plate 92 on an end of a cylindrical part 91, and an internal thread 94 is formed on the internal surface of a cylindrical part 91. In addition, each connector 9 presses the flanges 73 and 83 of the connecting rods 7 and 8 as a result of threadably engaging the internal threads 94 with the external threads 25 of the insulating rod 2. Numeral 85 is a lock nut for the main body of connecting rod 84.
The conventional insulation-operating rod for the porcelain-clad type circuit breaker is constructed as described above, in which the insulating rod 2 is threadably connected to the connecting rod 7 and 8. Accordingly, it is required that the connector 9 is designed to be considerably larger than the external diameter of the insulating rod 2. As a result, it is also required that the internal diameter of a pressure vessel accommodating the insulation-operating rod is larger. It is further required that length of the connector 9 along with the longitudinal axis is long enough to secure a required length of each thread, which influences connection strength between the insulating rod 2 and the connecting rods 7 and 8. Therefore, the conventional insulation-operating rod for the porcelain-clad circuit breaker has a problem in that not only weight influencing the operating characteristics is heavy but also cost of the parts is high.
Moreover, the conventional insulation-operating rod has following various problems. That is, manufacturing cost of the parts tends to be high because of need of applying threads to the insulating rod 2, connecting rods 7, 8 and connector 9. Adhesive coating on the threaded portions is also required to ensure coupling strength in such screw-thread coupling. There is a possibility of dispersion in mechanical strength as a result of uneven assembling. Man hour for assembling increases.
The present invention has been made to solve the above-discussed problems and has an object providing an insulation-operating rod having stable mechanical characteristics and electrical characteristics and capable of being compact as compared with the prior art.
According to one aspect of the invention, an insulation-operating rod includes a cylindrical insulating rod composed of an electrically insulating material, and a pair of connecting rods having a first shield portion for electric field relaxation on one end of each connecting rod. The first shield portion of the connecting rod and an end portion of the connecting rod continuous to the first shield portion are respectively inserted in an inserted end receiving portion of the insulating rod for receiving the inserted ends. Each connecting rod and the insulating rod are provided with a second shield portion for electric field relaxation on the external surface thereof, and are connected to each other through a metallic shield ring in which the inserted end receiving portion of said insulating rod is inserted and by a connecting pin passing through the metallic shield ring, the inserted end receiving portion and the end portion of the connecting rod.
As a result, since the insulating rod and the connecting rod are connected by the metallic shield rings and the connecting pins, any threading of the components is not necessary. Further, the insulating rod and connecting rod can be small-sized and light-weighted as compared with those used in the conventional insulation-operating rod. Furthermore, although any adhesive is applied to the thread in order to secure a mechanical strength of the thread-engaging portion in the prior art, any such application of adhesive is not required due to the connection with pin, making it possible to reduce man-hour for coating. As a result, it is now possible to achieve a light-weight, small-size, and cost-saving insulation-operating rod. Further, in the case of applying the insulation-operating rod according to the invention to a pressure vessel of a breaker, it becomes possible to make a pressure vessel light-weighted and small-sized as compared with the conventional one. Accordingly, it becomes possible to apply a smaller-sized operating system having smaller output than that of the prior art, which results in cost reduction of the breaker. Furthermore, the insulation-operating rod according to the invention is superior in electric characteristics, particularly in electrical insulation performance at portions to which direct current is applied.
It is preferable that the insulation-operating rod according to the invention is provided with a first gap and a second gap for preventing flashover respectively disposed between the end portion of the connecting rod and the inserted end receiving portion as well as between the metallic shield ring and the inserted end receiving portion; and further includes clearance change preventing means for preventing clearance change such as metallic spacer ring, metallic bushing or any other specific structure.
As a result, each clearance of the first gap and the second gap is maintained stable for a long time, thereby improving reliability in the electric characteristics of the insulation-operating rod.
In the insulation-operating rod according to the invention, it is preferable that the clearance change preventing means is a metallic spacer ring inserted between the metallic shield ring and the inserted end receiving portion as well as between the end portion of the connecting rod and the inserted end receiving portion.
In the insulation-operating rod according to the invention, it is also preferable that the clearance change preventing means is a metallic bushing in which the connecting pin is inserted, one end of the bushing coming in contact with the metallic shield ring, and another end of each bushing coming in contact with the end portion of the connecting rod.
In the insulation-operating rod according to the invention, it is also preferable that the clearance change preventing means has a construction in which at least a part of facing surface of the metallic shield ring and that of the inserted end receiving portion, and at least a part of opposed face of the end portion of the connecting rod and that of the inserted end receiving portion, are close to or in contact with each other within a range of not substantially producing any play clearance.